GPZ 7000 Tear-down

[jasong]

I'm glad you are still working on the big drag coils, I'd really like to see one of those in action sometime if we happen to be in the same place and same time again. One of those would be fun to drag around some of the washes in Arizona that are deep and produced some bigger nuggets. 

I have my old 4500 still and I'd like to put it to use for something like that eventually, rather than just sitting in the closet. 

Is there any consideration for those big drag coils other than just getting the electrical characteristics (inductance, resistance, internal capacitance, etc) matching within some tolerance, proper shielding, and then plug them in and they should work? For the drag coils I imagine you have to find a way to keep them pretty rigid still?

[phrunt]

I recall X-coils made @davsgold a drag coil for the GPZ, well I think they did, perhaps it was just a plan that never went ahead I don't remember. 

I can't remember the reason but @Reg Wilson who is a big drag coil person always said the GPX 4000 was the better drag coil detector over the 4500, something to do with EMI from the Quad bike I think it was.... a long time ago I read that post. 

The GPZ should be quite a good drag coil detector you would think being better with EMI than the GPX's, I doubt Woodys mods would improve the drag coil EMI situation as the giant coil would be the source of most EMI along with the Quad bike alternator and whatever else associated with the bike.

[Reg Wilson]

Back in 1990 I was sharing a house with John Hider Smith and Ian Jacques just out of  Maryborough in central Victoria. We were involved in testing a new type of metal detector called pulse induction when Bruce Candy paid us a visit with an experimental system that he had been working on. This involved a large cable that would loop around a patch of ground that was suspected of holding big gold at a depth that conventional detectors would be incapable of hearing.

The idea was to have this Tx cable connected to the electronics while an operator would work within the circle of of cable with what appeared to be a conventional hand held detector, but would only be Rx. Hopefully the Tx would be powerful enough to induce a strong electro magnetic field within the loop, while the Rx would pick up the target response when passed over it.

My memory is a bit foggy on  the results, but for whatever reason it was not a 'goer'. In those days Bruce was always thinking of new ways to achieve results.

[Chet]

    Large coils are on the back burner for now. Below is the second one 58" x 28" that I put together. The electrical specifications are the same as standard coils. I wound both the transmitter and receiver with wide spacing between turns. This cuts down the coil capacitance and improves the Q (quality) of the coils.
    It started out to be a drag coil but since I don’t have a ATV and Northern Nevada has so much sage brush it became a large push and pull coil. It weights approximately nine pounds. It has some serious problems that prevent it from being a good coil. My pick, the detector body and other stuff are too close to the coil. Going over rising and falling ground sounds similar to swinging over damp salty ground. The coil cable sounds off when it is moved up and down. The windings are glued down and the foam board is rigid so it doesn’t have any bumping noise.
     It picks up shallow .22 bullets as double hits as each receiver coil passes over them. Air testing above the coil; one ounce gold coin around two feet; coke can approximately seven feet.
     Since coke can size nuggets are so rare I am working on 25 to 30 inch coils. Improving depth on one ounce and below is the goal.
 

[jasong]

2 hours ago, Reg Wilson said:

Back in 1990 I was sharing a house with John Hider Smith and Ian Jacques just out of  Maryborough in central Victoria. We were involved in testing a new type of metal detector called pulse induction when Bruce Candy paid us a visit with an experimental system that he had been working on. This involved a large cable that would loop around a patch of ground that was suspected of holding big gold at a depth that conventional detectors would be incapable of hearing.

The idea was to have this Tx cable connected to the electronics while an operator would work within the circle of of cable with what appeared to be a conventional hand held detector, but would only be Rx. Hopefully the Tx would be powerful enough to induce a strong electro magnetic field within the loop, while the Rx would pick up the target response when passed over it.

My memory is a bit foggy on  the results, but for whatever reason it was not a 'goer'. In those days Bruce was always thinking of new ways to achieve results.

Ah nice...Candy's idea there is exactly what I was thinking about myself. Bummer it doesn't work. I'd be curious if you have any old notes from that experiment what the problems were and if they were surmountable. I'd see it being hard to sell and limited customer base, if that was the problem then I might try myself, but if it has physical/engineering problems then there is nothing I could do any better than Bruce Candy did so no point trying.

Interesting to hear it was tried though, thanks. 

43 minutes ago, Chet said:

    Large coils are on the back burner for now. Below is the second one 58" x 28" that I put together. The electrical specifications are the same as standard coils. I wound both the transmitter and receiver with wide spacing between turns. This cuts down the coil capacitance and improves the Q (quality) of the coils.
    It started out to be a drag coil but since I don’t have a ATV and Northern Nevada has so much sage brush it became a large push and pull coil. It weights approximately nine pounds. It has some serious problems that prevent it from being a good coil. My pick, the detector body and other stuff are too close to the coil. Going over rising and falling ground sounds similar to swinging over damp salty ground. The coil cable sounds off when it is moved up and down. The windings are glued down and the foam board is rigid so it doesn’t have any bumping noise.
     It picks up shallow .22 bullets as double hits as each receiver coil passes over them. Air testing above the coil; one ounce gold coin around two feet; coke can approximately seven feet.
     Since coke can size nuggets are so rare I am working on 25 to 30 inch coils. Improving depth on one ounce and below is the goal.

That's awesome Chet! Haha I love it...even if it didn't work as you'd hoped. The spirit of experimentation is great. Don't ever get rid of that coil, I'll take it if you are going to throw it away! 😁 👌

Yeah it's hard to find a place to imagine a drag coil being able to be ultra useful due to all the brush. I'd like to try dragging one down some of those Gold Basin deep washes where I know some larger stuff came out of, just flat sandy 4ft wide washes, all about 2-4ft deep. I had a backhoe in one wash and I was hitting deep little pockets that had nuggets at like 5-6ft deep, but they were like 2 grams max. Unfortunately most of the big nuggets I know of came out of washes you can't run a coil that big, but there are a few... I know a few places where some 4-10 ouncers came off hillsides that are kinda deep too, but a bunch of people pretty much claimed all that stuff after Jeff Williams came in and started doing gold tours on all the old dead patches like a dodo. 

How deep will that 58x28" hit a .22? Mostly just near surface? 

I have the 22" X Coil CC that I'm dying to try out, but all my ground this summer is not very deep so I might have to wait until winter to really give it a workout in NV or AZ. 

[Reg Wilson]

Being 33 years ago, my memory of the details of Bruce's experiment is not great, but he certainly had some intriguing ideas. At one time he developed a system that could tell definitely whether a tennis ball was inside the line or not.

This involved a wire mesh beneath the court and balls impregnated with metal. A clever but expensive concept that got as far as a prototype before the far less expensive 'Hawkeye' system was developed and accepted. I have a foggy recollection of a partner being involved in that project who left Bruce holding all the debt involved.

Another experiment that I was involved in was the EMDAR (electronic metal detecting and recovery) project. This was a hopper (with grizzly's) that fed a conveyer belt with a metal detector (VLF in those days) positioned beneath the belt. When a signal was detected a gate at the end of the belt directed that portion of material into a holding drum before returning to directing into the reject heap. The whole apparatus was on skids so that it could be moved with the use of a backhoe - loader which also fed the hopper and moved the reject pile as it accumulated.

The whole idea was to use EMDAR to separate oversize material in a mining operation. I had access to a deep lead mullock heap that contained metal (gads, machinery bits, broken picks etc). It also had quite a few bits of gold up to an ounce and even better.  This had been a very rich mine and the miners had been a bit careless with recovery. There were a few bugs in the system, but eventually it was up and away. 

At the end of a trial period I used a small dozer that I owned at the time to push out a similar amount of material and detect it by hand. I then pushed out the EMDAR reject heap. The result was that it took less time to push, detect and then re pile the material than to put it through the EMDAR and this method also recovered metal (gold included) in the reject heap that EMDAR had missed.

I then made the mistake of voicing the opinion that they had developed 'technology for technologies' sake'. I should have shut up as I could tell that the Minelab crew were not impressed with me. 'Shoot the messenger". Minelab went on to actually persevere with EMDAR and I did see one unit for sale in a mining magazine at one time. I remember that the machinery was priced at Au$80,000 new. I have no idea of how many were built.

Up until that point I had been fairly closely involved with Minelab, but after not quite much so. Possibly just coincidence.

What not many people know is that Bruce's passion was not metal detectors at all, but HiFi, and he went on to develop high end sound systems.

[Chet]

On 5/3/2023 at 4:59 PM, jasong said:

How deep will that 58x28" hit a .22? Mostly just near surface?

Yes the .22 bullets were just a few inches deep.

My latest coils to be tested the next time in the field are below. One is a 6” mono for the GPX 6000.The other is a 8” concentric for the GPZ 7000.
 

[phrunt]

8" Concentric is a small concentric for the GPZ,  I'd like that size coil, the smallest X-coils made was a 12" but it was never released for sale, I have one however, I think it's great, it's bundle wound as spiral would not fit.

It's great you're making these coils Chet, Please keep us all updated on your progress.

[jasong]

For the smaller concentrics, is it possible to have enough space for flat windings in a smaller coil by stacking them on top of each other into some kind of quasi-concentric? Or does the produce capacitance issues? Or it wouldn't really work as a concentric (since they aren't technically concentric)? Would that arrangement be useful at all for something, or no?

Woody's talking about cable capacitance also makes me wonder if XP has the right idea at least in part by putting the RX circuitry in the coil itself. That way only the TX would need a cable from the control box and the capacitance of the cable shouldn't matter since the RX isn't passed through it. That should allow a quicker sampling time, and thus more sensitivity to faster transient targets, etc. Curious if Minelab might look at that idea in future gold detectors, or if it's even feasible with PIs. 

[Chet]

2 hours ago, jasong said:

For the smaller concentrics, is it possible to have enough space for flat windings in a smaller coil by stacking them on top of each other into some kind of quasi-concentric? Or does the produce capacitance issues? Or it wouldn't really work as a concentric (since they aren't technically concentric)? Would that arrangement be useful at all for something, or no?

Woody's talking about cable capacitance also makes me wonder if XP has the right idea at least in part by putting the RX circuitry in the coil itself. That way only the TX would need a cable from the control box and the capacitance of the cable shouldn't matter since the RX isn't passed through it. That should allow a quicker sampling time, and thus more sensitivity to faster transient targets, etc. Curious if Minelab might look at that idea in future gold detectors, or if it's even feasible with PIs. 

      The majority of pulse inductance detectors are designed to operate with coils that have an inductance of 300 microhenries with a resistance of less than 0.5 ohms and less than 400 picofarads of coil and lead capacitance. A small coil requires almost as many feet of heavy gauge wire as a large coil to meet required specifications. This means that the small coil space severely limits winding forms. My six inch GPX 6000 mono coil (below) required two flat wound layers which fill up the housing. The eight inch GPZ 7000 concentric coil (also below) was accomplished by stacking the windings vertically which doubled the height of the coil.
       A coil lead is approximately 50 to 100 picofarads which is considerably less than normal coil capacitance. Moving the receiver or preamplifier into a pulse induction coil is more of a problem than with a VLF detector. It would also make aftermarket coils very difficult and expensive. 
        The GPX 6000 coils are very sensitive to small and tiny nuggets. There is more to gain in signal and EMI processing than in coil design.